- Synthesis of β-Silyl-α-amino Acid Derivatives by Cu-Catalyzed Regio- and Enantioselective Silylamination of α,β-Unsaturated Esters
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A copper-catalyzed silylamination of α,β-unsaturated esters with silylboranes and hydroxylamines has been developed to afford the corresponding β-silyl-α-amino acid derivatives, which are of great interest in medicinal and pharmaceutical chemistry. Additionally, by using a suitable chiral bisphosphine ligand, the asymmetric induction is possible, delivering the optically active β-silyl-α-amino acids with synthetically acceptable diastereomeric ratios (55:45-82:18 dr) and high enantiomeric ratios (81:19-99:1 er).
- Hirano, Koji,Kobayashi, Toshimichi,Miura, Masahiro,Nishino, Soshi
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supporting information
(2022/02/14)
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- Unlocking the Accessibility of Alkyl Radicals from Boronic Acids through Solvent-Assisted Organophotoredox Activation
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Despite their prevalence in organic synthesis, the application of boronic acids (BAs) as alkyl radical precursors in visible-light-assisted photocatalyzed reactions has been limited by their high oxidation potential. This study demonstrates the prominent
- Ranjan, Prabhat,Pillitteri, Serena,Coppola, Guglielmo,Oliva, Monica,Van der Eycken, Erik V.,Sharma, Upendra K.
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p. 10862 - 10870
(2021/09/08)
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- An umpolung-enabled copper-catalysed regioselective hydroamination approach to α-amino acids
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A copper-catalysed regio- and stereoselective hydroamination of acrylates with hydrosilanes and hydroxylamines has been developed to afford the corresponding α-amino acids in good yields. The key to regioselectivity control is the use of hydroxylamine as
- Hirano, Koji,Miura, Masahiro,Nishino, Soshi
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p. 11525 - 11537
(2021/09/07)
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- Photocatalyzed, β-Selective Hydrocarboxylation of α,β-Unsaturated Esters with CO2under Flow for β-Lactone Synthesis
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A photocatalyzed, β-selective hydrocarboxylation of α,β-unsaturated esters employing CO2 radical anion generated under flow conditions was developed. A range of substrates bearing a variety of functional groups were tolerated, demonstrating chemoselectivity. A series of quaternary carboxylic acids were obtained from sterically demanding β,β-disubstituted alkenes including those derived from natural products. Mechanistic studies support a Giese-type CO2 radical anion conjugate addition followed by hydrogen atom transfer from (TMS)3SiH as the principal reaction pathway. Finally, a telescoped process involving the described β-carboxylation followed by a α-bromination/β-lactonization sequence provides a strategy for β-lactone synthesis.
- Kang, Guowei,Romo, Daniel
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p. 1309 - 1315
(2021/02/01)
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- An Iron-Mesoionic Carbene Complex for Catalytic Intramolecular C-H Amination Utilizing Organic Azides
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The synthesis of N-heterocycles is of paramount importance for the pharmaceutical industry. They are often synthesized through atom economic and environmentally unfriendly methods, generating significant waste. A less explored, but greener, alternative is
- Albrecht, Martin,Keilwerth, Martin,Meyer, Karsten,Pividori, Daniel M.,Stroek, Wowa
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supporting information
p. 20157 - 20165
(2021/12/09)
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- Two-way homologation of aliphatic aldehydes: Both one-carbon shortening and lengthening via the same intermediate
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Aliphatic aldehydes can be homologated to both one-carbon shorter and one-carbon longer homologous carbonyl compounds through the 2–4 steps of reactions via the same intermediates, β,γ-unsaturated α-nitrosulfones, prepared from the proline-catalyzed sequential reactions of several aliphatic aldehydes with phenylsulfonylnitromethane. While the oxidative cleavage of the key intermediates gave one-carbon less homologous carbonyl compounds, the reduction of the same key intermediates followed by an oxidation produced one-carbon more homologous carbonyl compounds.
- Yoo, Jae Won,Seo, Youngran,Park, Jong Beom,Kim, Young Gyu
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- Iron-catalysed 1,2-aryl migration of tertiary azides
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1,2-Aryl migration of α,α-diaryl tertiary azides was achieved by using the catalytic system of FeCl2/N-heterocyclic carbene (NHC) SIPr·HCl. The reaction generated aniline products in good yields after one-pot reduction of the migration-resultant imines.
- Wei, Kaijie,Yang, Tonghao,Chen, Qing,Liang, Siyu,Yu, Wei
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supporting information
p. 11685 - 11688
(2020/10/19)
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- Cobalt(II)-Catalyzed Alkoxycarbonylation of Aliphatic Amines via C-N Bond Activation
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The first cobalt-catalyzed deaminative alkoxycarbonylation reaction was described for the conversion of readily available primary alkyl amines to synthetically versatile esters with moderate to high yields. This transformation shows good functional group compatibility and can serve as a powerful tool for the modification of alkyl amine-containing complex natural products and drug molecules.
- Li, Chong-Liang,Jiang, Xuan,Lu, Liang-Qiu,Xiao, Wen-Jing,Wu, Xiao-Feng
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p. 6919 - 6923
(2019/09/07)
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- N-Heterocyclic Carbene Iron(III) Porphyrin-Catalyzed Intramolecular C(sp3)–H Amination of Alkyl Azides
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Metal-catalyzed intramolecular C?H amination of alkyl azides constitutes an appealing approach to alicyclic amines; challenges remain in broadening substrate scope, enhancing regioselectivity, and applying the method to natural product synthesis. Herein we report an iron(III) porphyrin bearing axial N-heterocyclic carbene ligands which catalyzes the intramolecular C(sp3)–H amination of a wide variety of alkyl azides under microwave-assisted and thermal conditions, resulting in selective amination of tertiary, benzylic, allylic, secondary, and primary C?H bonds with up to 95 % yield. 14 out of 17 substrates were cyclized selectively at C4 to give pyrrolidines. The regioselectivity at C4 or C5 could be tuned by modifying the reactivity of the C5–H bond. Mechanistic studies revealed a concerted or a fast re-bound mechanism for the amination reaction. The reaction has been applied to the syntheses of tropane, nicotine, cis-octahydroindole, and leelamine derivatives.
- Shing, Ka-Pan,Liu, Yungen,Cao, Bei,Chang, Xiao-Yong,You, Tingjie,Che, Chi-Ming
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supporting information
p. 11947 - 11951
(2018/09/11)
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- Hydrogen-transfer reduction of α,β-unsaturated carbonyl compounds catalyzed by naphthyridine-functionalized N-heterocyclic carbene complexes
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Substitution of silver complex of 2-chloro-7-(mesitylimidazolylidenylmethyl)naphthyridine (NpNHC) with palladium(II), rhodium(I) and iridium(I) metal precursors provided [Pd(C,N-NpNHC)(η3-allyl)](BF4) (5), RhCl(COD)(C-NpNHC) (6a) and IrCl(COD)(C-NpNHC) (6b), respectively. Abstraction of chloride from 6a and 6b with AgBF4 provided the chelation complexes [Rh(COD)(C,N-NpNHC)](BF4) (7a) and Ir(COD)(C,N-NpNHC)(BF4) (7b), respectively. All complexes were characterized using NMR and elemental analyses and the structural details of 5 and 6a were further confirmed using X-ray crystallography. In catalytic activity studies, complex 5 was found to be an effective catalyst in the hydrogen-transfer reduction of α,β-unsaturated carbonyl compounds into the corresponding saturated carbonyl compounds.
- Huang, Hsiao-Ching,Ramanathan, Mani,Liu, Yi-Hong,Peng, Shie-Ming,Liu, Shiuh-Tzung
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- Alkyl?(Hetero)Aryl Bond Formation via Decarboxylative Cross-Coupling: A Systematic Analysis
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Suzuki, Negishi, and Kumada couplings are some of the most important reactions for the formation of skeletal C?C linkages. Their widespread use to forge bonds between two aromatic rings has enabled every branch of chemical science. The analogous union between alkyl halides and metallated aryl systems has not been as widely employed due to the lack of commercially available halide building blocks. Redox-active esters have recently emerged as useful surrogates for alkyl halides in cross-coupling chemistry. Such esters are easily accessible through reactions between ubiquitous carboxylic acids and coupling agents widely used in amide bond formation. This article features an amalgamation of in-house experience bolstered by approximately 200 systematically designed experiments to accelerate the selection of ideal reaction conditions and activating agents for the cross-coupling of primary, secondary, and tertiary alkyl carboxylic acids with both aryl and heteroaryl organometallic species.
- Sandfort, Frederik,O'Neill, Matthew J.,Cornella, Josep,Wimmer, Laurin,Baran, Phil S.
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supporting information
p. 3319 - 3323
(2017/03/17)
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- Redox-Active Esters in Fe-Catalyzed C-C Coupling
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Cross-couplings of alkyl halides and organometallic species based on single electron transfer using Ni and Fe catalyst systems have been studied extensively, and separately, for decades. Here we demonstrate the first couplings of redox-active esters (both isolated and derived in situ from carboxylic acids) with organozinc and organomagnesium species using an Fe-based catalyst system originally developed for alkyl halides. This work is placed in context by showing a direct comparison with a Ni catalyst for >40 examples spanning a range of primary, secondary, and tertiary substrates. This new C-C coupling is scalable and sustainable, and it exhibits a number of clear advantages in several cases over its Ni-based counterpart.
- Toriyama, Fumihiko,Cornella, Josep,Wimmer, Laurin,Chen, Tie-Gen,Dixon, Darryl D.,Creech, Gardner,Baran, Phil S.
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p. 11132 - 11135
(2016/10/12)
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- Structure-Based Design of Potent Nicotinamide Phosphoribosyltransferase Inhibitors with Promising in Vitro and in Vivo Antitumor Activities
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Inhibition of nicotinamide phosphoribosyltransferase (NAMPT) has the potential to directly limit NAD production in cancer cells and is an effective strategy for cancer treatment. Using a structure-based strategy, we have designed a new class of potent small-molecule inhibitors of NAMPT. Several designed compounds showed promising antiproliferative activities in vitro. (E)-N-(5-((4-(((2-(1H-Indol-3-yl)ethyl)(isopropyl)amino)methyl)phenyl)amino)pentyl)-3-(pyridin-3-yl)acrylamide, 30, bearing an indole moiety, has an IC50 of 25.3 nM for binding to the NAMPT protein and demonstrated promising inhibitory activities in the nanomolar range against several cancer cell lines (MCF-7 GI50 = 0.13 nM; MDA-MB-231 GI50 = 0.15 nM). Triple-negative breast cancer is the most malignant subtype of breast cancer with no effective targeted treatments currently available. Significant antitumor efficacy of compound 30 was achieved (TGI was 73.8%) in an orthotopic MDA-MB-231 triple-negative breast cancer xenograft tumor model. This paper reports promising lead molecules for the inhibition of NAMPT which could serve as a basis for further investigation.
- Bai, Jinhong,Liao, Chenzhong,Liu, Yanghan,Qin, Xiaochu,Chen, Jiaxuan,Qiu, Yatao,Qin, Dongguang,Li, Zheng,Tu, Zheng-Chao,Jiang, Sheng
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supporting information
p. 5766 - 5779
(2016/07/06)
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- Lewis Base Activation of Silyl Acetals: Iridium-Catalyzed Reductive Horner-Wadsworth-Emmons Olefination
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A Lewis base promoted deprotonative pronucleophile addition to silyl acetals has been developed and applied to the iridium-catalyzed reductive Horner-Wadsworth-Emmons (HWE) olefination of esters and the chemoselective reduction of the resulting enoates. Lewis base activation of silyl acetals generates putative pentacoordinate silicate acetals, which fragment into aldehydes, silanes, and alkoxides in situ. Subsequent deprotonative metalation of phosphonate esters followed by HWE with aldehydes furnishes enoates. This operationally convenient, mechanistically unique protocol converts the traditionally challenging aryl, alkenyl, and alkynyl esters to homologated enoates at room temperature within a single vessel.
- Dakarapu, Udaya Sree,Bokka, Apparao,Asgari, Parham,Trog, Gabriela,Hua, Yuanda,Nguyen, Hiep H.,Rahman, Nawal,Jeon, Junha
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supporting information
p. 5792 - 5795
(2015/12/11)
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- SUBSTITUTED BENZOXAZOLONE DERIVATIVES AS ACID CERAMIDASE INHIBITORS, AND THEIR USE AS MEDICAMENTS
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The present invention relates to substituted benzoxazolone derivatives as acid ceramidase inhibitors, pharmaceutical compositions containing these inhibitors and methods of inhibiting acid ceramidase for the treatment of disorders in which modulation of the levels of ceramide is clinically relevant. The invention also provides substituted benzoxazolone derivatives for use in the treatment of cancer, inflammation, pain, inflammatory pain or pulmonary diseases.
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- Sunlight-driven trifluoromethylation of olefinic substrates by photoredox catalysis: A green organic process
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The principles and utility of photoredox catalysis in organic synthesis are described. After a brief description of the features of the two types of catalytic photoredox processes following the reductive quenching cycle (RQC) and the oxidative quenching cycle (OQC), the discussion is focused on organic transformations based on OQC, in particular the trifluoromethylation of olefinic substrates with electrophilic trifluoromethylating reagents furnishing solvolytic addition products and substitution products. It is concluded that catalytic photoredox systems are green from the point of view of harmfulness, safety, and energy source (visible light, including sunlight). Future prospects of photoredox catalysis will be also discussed.
- Akita, Munetaka,Koike, Takashi
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p. 742 - 751
(2015/07/15)
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- Ultrasound-Assisted Methyl Esterification of Carboxylic Acids ACatalyzed by Polymer-Supported Triphenylphosphine
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A convenient and efficient sonochemical method for methyl esterification of carboxylic acids catalyzed by polymer-supported triAphenylphosphine (PS-Ph3P) is reported. In the presence of 1:0.1:2 molar ratio of 2,4,6-trichloro-1,3,5-triazine/PS-Ph3P/Na2CO3, methyl esters of various carboxylic acids bearing reactive hydroxyl groups as well as acid-or base-labile functionalities could be rapidly prepared (within 10-20 min) in good to excellent yields without necessity to pre-activate the acids. Using the polymer-bound phosphine also allows easy isolation of the products which, in most of the cases, were obtained in high purities without column chromatography.
- Jaita, Subin,Phakhodee, Wong,Pattarawarapan, Mookda
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p. 2006 - 2008
(2015/09/01)
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- Transition-metal-free and chemoselective NaOtBu-O 2-mediated oxidative cleavage reactions of vic-1,2-diols to carboxylic acids and mechanistic insight into the reaction pathways
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A method for efficient oxidative cleavage of vic-1,2-diols using a NaO tBu-O2 system resulted in the formation of carboxylic acids in high yields. The present protocol is an eco-friendly alternative to a conventional transition-metal-based method. This new strategy allows large-scale production with nonchromatographic purification while also suppressing competitive reaction pathway such as benzilic acid rearrangement.
- Kim, Sun Min,Kim, Dong Wan,Yang, Jung Woon
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p. 2876 - 2879
(2014/06/23)
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- Visible light-induced selective generation of radicals from organoborates by photoredox catalysis
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A new strategy for the generation of carbon-centered radicals via oxidation of alkyl-, allyl-, benzyl- and arylborates by visible-light-driven single electron transfer (SET) photoredox catalysis has been established. The generated radicals smoothly react with TEMPO and electron-deficient alkenes to afford C-O and C-C coupling products, respectively. In this radical initiating system, cyclic organo(triol)borates turn out to be useful radical precursors.
- Yasu, Yusuke,Koike, Takashi,Akita, Munetaka
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p. 3414 - 3420
(2013/02/25)
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- Regioselective 1,2,3-bisazfulleroid: Doubly N-bridged bisimino-PCBMs for polymer solar cells
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The direct bisaddition of methyl 5-azido-5-phenylpentanoate to C60takes place in the two neighboring pentagon-hexagon junctions of the same five-membered ring, yielding a regioselective bisazfulleroid, namely bisimino-PCBM. Because of its open
- Kim, Boram,Lee, Junghoon,Seo, Jung Hwa,Wudl, Fred,Park, Sung Heum,Yang, Changduk
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p. 22958 - 22963
(2013/01/15)
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- The non-metathetic role of Grubbs' carbene complexes: From hydrogen-free reduction of α,β-unsaturated alkenes to solid-supported sequential cross-metathesis/reduction
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An efficient and high-yielding "hydrogen-free" reduction of α,β-unsaturated alkenes was carried out employing Grubbs' catalyst in a non-metathetic role and Et3SiH. Conditions were optimized under microwave irradiation. Application to the solid-phase organic synthesis allows a facile construction of sp3-sp3 carbon bonds through a sequential cross metathesis/olefin reduction.
- Poeylaut-Palena, Andres A.,Testero, Sebastian A.,Mata, Ernesto G.
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supporting information; experimental part
p. 1565 - 1567
(2011/03/20)
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- CARBOXYLIC DERIVATIVES FOR USE IN THE TREATMENT OF CANCER
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The invention provides novel compounds of formula (I), wherein: R1 is a radical derived from one of the known ring systems; R2 is a phenyl radical optionally substituted; Xn represents a birradical selected from the group consisting of: -(CH2)1-4-, (C2-C4)-alkenyl, (C2-C4)alkynyl, -S-(CH2)1-3-#, and -(CH2)1-3-O-#; wherein the symbol # indicates the position at which Xn is attached to R1; Yn is a birradical selected from the group consisting of: -(CH2)2-4-, -S-(CH2)1-3#, and -O-(CH2)1-3-#,; where in the symbol # indicates the position at which Yn is attached to R2; and R3 is a radical selected from the group consisting of: -OR4. The compounds of formula (I) are useful in the treatment of cancer
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Page/Page column 56
(2009/07/25)
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- Disulfide symmetric dimers as stable pre-hapten forms for bioconjugation: A strategy to prepare immunoreagents for the detection of sulfophenyl carboxylate residues in environmental samples
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A convenient, generic synthesis of bioconjugates from haptens with a thiol group has been established. The corresponding haptens are synthesized as stable symmetric dimmers through a disulfide bond that is reduced immediately before conjugation with the a
- Estevez, M.-Carmen,Galve, Roger,Sanchez-Baeza, Francisco,Marco, M.-Pilar
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experimental part
p. 1906 - 1917
(2009/04/08)
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- Pd-C-induced catalytic transfer hydrogenation with triethylsilane
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(Chemical Equation Presented) In situ generation of molecular hydrogen by addition of triethylsilane to palladium-charcoal catalyst results in rapid and efficient reduction of multiple bonds, azides, imines, and nitro groups, as well as benzyl group and allyl group deprotection under mild, neutral conditions.
- Mandal, Pijus K.,McMurray, John S.
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p. 6599 - 6601
(2008/02/10)
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- Cobalt-catalyzed reductive coupling of saturated alkyl halides with activated alkenes
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An efficient cobalt-catalyzed reductive coupling reaction of alkyl halides with electron-withdrawing alkenes (CH2=CR1EWG, EWG = electron-withdrawing group) in the presence of water and zinc powder in acetonitrile to give the corresponding Michael-type addition product (RCH 2CR1EWG) was described. The methodology is versatile such that unactivated primary, secondary, and tertiary alkyl bromides and iodides and various conjugated alkenes including acrylates, acrylonitrile, methyl vinyl ketone, and vinyl sulfone all successfully participate in this coupling reaction. For the alkyl halides used in the reaction, the iodides generally gave heller yields compared to those of the corresponding bromides. It is a unique method employing CoI2dppe, zinc, and alkyl halides, affording conjugate addition products in high yields. Mechanistically, the reaction appears to follow an oxidative addition driven route rather than the previously reported radical route.
- Shukla, Paritosh,Hsu, Yun-Chu,Cheng, Chien-Hong
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p. 655 - 658
(2007/10/03)
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- A new robust and highly sensitive FRET donor-acceptor pair: Synthesis, characterization, and application in a thrombin assay
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The synthesis of a new, robust fluorescence-resonance-energy-transfer (FRET) system is described. Its donor chromophore is derived from an N-allyl-substituted quinolinone attached to 4-bromophenyl-alanine via Heck cross-coupling. The resulting Fmoc-protected derivative 11 was used as building block in solid-phase peptide synthesis (SPPS). As FRET acceptor, a sulfonylated ruthenium(II)-bathophenanthroline complex with a peripheral COOH function was prepared for covalent attachment to target molecules. The UV/VIS absorption and emission spectra of peptides bearing only the donor (D) or acceptor (A) dye showed a good overlap of the emission band of the donor with the absorption band of the acceptor. The fluorescence spectra of a peptide bearing both dyes revealed an additional emission after excitation of the donor, which is due to indirect excitation of the acceptor via FRET. The long fluorescence lifetime of the RuII complex (0.53 μs) makes it well-suited for time-resolved measurements. As a first application of this new FRET system, the peptide 18, with the recognition sequence for the protease thrombin, flanked by the two dyes, was synthesized and successfully cleaved by the enzyme. The change in the ratio of the fluorescence intensities could be determined.
- Kainmueller, Eva K.,Bannwarth, Willi
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p. 3056 - 3070
(2008/01/27)
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- HISTONE DEACETYLASE INHIBITORS
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Hormone refractory metastatic disease can be treated with an oxyamide-containing compound through the inhibition of HDAC1 or HDAC2.
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Page/Page column 31
(2008/06/13)
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- Rhodium-catalyzed cascade reactions: A methylenation-hydroboration homologative process
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A very efficient rhodium-catalyzed cascade process allowing the transformation of aldehydes and ketones into their corresponding one or two-carbon homologated alcohol products through a methylenation-hydroboration sequence is reported. Wilkinson's complex is used to catalyze both reactions in a one-pot procedure that does not require the isolation of the alkene intermediate.
- Lebel, Hélène,Ladjel, Chehla
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p. 5198 - 5205
(2007/10/03)
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- Histone deacetylase inhibitors
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Histone deacetylase is a metallo-enzyme with zinc at the active site. Compounds having a zinc-binding moiety, such as, for example, a carboxylic acid group, can inhibit histone deacetylase. Histone deacetylase inhibition can repress gene expression, inclu
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- Intramolecular Cyclization of Acyl Radicals onto the Azido Group: A New Radical Approach to Cyclized Lactams
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(Equation Presented) Reagents: i, Bu3SnH/AlBN; ii, (TMS)3SiH/AlBN. Aryl- and alkyl-derived azidoacyl radicals, generated from thiolesters by intramolecular homolytic substitution at the sulfur, can undergo five- and six-membered cyclization onto the azido moiety to give cyclized lactams.
- Benati, Luisa,Leardini, Rino,Minozzi, Matteo,Nanni, Daniele,Spagnolo, Piero,Strazzari, Samantha,Zanardi, Giuseppe
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p. 3079 - 3081
(2007/10/03)
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- Selective Mono- and Bis(alkoxycarbonylation)s of Olefins Catalyzed by Palladium in the Presence of Cu(I) or Cu(II) Chloride under Remarkably Mild Conditions. Application to the Synthesis of γ-Butyrolactone Derivatives
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Palladium-catalyzed mono- and bis(alkoxycarbonylation)s of the olefins were controlled by the use of copper(II) and copper(I) chloride, respectively, in alcohol under normal pressure of carbon monoxide and oxygen at room temperature without any other additives. 3-Buten-1-ols gave the corresponding γ-butyrolactones and 2-oxotetrahydrofuran-3-acetic acid esters, respectively, in high yields.
- Toda, Shiho,Miyamoto, Masanori,Kinoshita, Hideki,Inomata, Katsuhiko
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p. 3600 - 3606
(2007/10/02)
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- A New Approach to Aromatic Substitution - para-Specific Alkylation of Acetophenone by Alkyl Radicals in Strongly Acidic Media
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Acetophenone in 25percent oleum is substituted by various alkyl radicals specifically in the para-position.The radicals used include cyclohexyl, 3-chloro-1-methylpropyl, 3-bromo-1-methylpropyl, 4-chloro-1-methylbutyl, 4-bromo-1-methylbutyl, 5-bromo-1-methylpentyl, 5-acetoxy-1-methylpentyl, 3-carboxy-1-methylpropyl, 4-carboxy-1-methylbutyl and 5-carboxy-1-methylpentyl.They were all generated by hydrogen atom abstraction at the radical position by dimethylaminium radicals, generated in turn from protonated dimethylchloramine and ferrous sulphate.Yields were generally poor to moderate but utilised simple conditions and cheap reagents.
- Din, Laily Bin,Meth-Cohn, Otto,Walshe, Nigel D. A.
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p. 781 - 786
(2007/10/02)
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- Selective Mono- and Dicarbonylation of Terminal Olefins Catalyzed by Pd-C in the Presence of Cu(II) or Cu(I) Chloride under Mild Conditions
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Pd-C can catalyze the carbonylation of terminal olefins with normal pressure of carbon monoxide at room temperature.The corresponding mono- and diesters (succinates) were selectively formed in excellent yields using Cu(II) and Cu(I) chloride, respectively, in alcohol.
- Inomata, Katsuhiko,Toda, Shiho,Kinoshita, Hideki
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p. 1567 - 1570
(2007/10/02)
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- Aspects of Tautomerism. 13. Alkaline Hydrolysis of γ-, δ-, and ε-Keto Esters and their Desoxy Analogues. Geometrical Constraints on Keto Participation
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The rates of alkaline hydrolysis of methyl β-benzoylpropionate (I), methyl γ-benzoylbutyrate (II) and methyl δ-benzoylvalerate (III) decrease in the order I>II>III.Keto participation is the predominant pathway in the case of γ-keto esters.Evidence has also been obtained for keto participation in the case of δ-keto esters, whereas no such evidence is available in the case of ε-keto esters studied.
- Bhatt, M. Vivekananda,Ravindranathan, M.,Somayaji, Viswanatha,Rao, G. Venkoba
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p. 3170 - 3173
(2007/10/02)
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- Carbanion Rearrangements by Intramolecular 1,ω Proton Shifts, III. The Reaction of 2-, 3-, 4-, and 5-Phenylalkyllithium Compounds
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Upon addition of THF to a solution of 4-phenylbutyllithium (2) in diethyl ether a rapid intramolecular 1,4 proton shift takes place with the formation of 1-phenylbutyllithium (5).Similarly, although somewhat more slowly, 5-phenylpentyllithium (82) rearranges to 1-phenylpentyllithium (83) via 1,5 proton transfer.The corresponding rearrangements by 1,2 or 1,3 hydrogen shifts, however, starting with 2-phenylethyllithium (1) and 3-phenylpropyllithium (54), respectively, were not detected.With 3-phenylpropyllithium (54) a slow intramolecular 1,5 transfer an ortho proton is observed instead, yielding o-propylphenyllithium (100).The corresponding 1,6 shift with 4-phenylbutyllithium (2) was also detected in a minor amount in addition to the 1,4 proton shift already mentioned.There is no indication, however, for a 1,4 transfer of an ortho proton in 2-phenylethyllithium (1).The reaction products in this case can be exclusively explained by intermolecular transmetallation reactions.All ω-phenylalkyllithium compounds under investigation show interesting side and secondary reactions being rather different in deuterated solvents and in deuteriumfree solvents, respectively, due to the isotope effects.The analysis of the products is accomplished by 1H-NMR spectroscopy and, after derivatization, with the help of a GC-MS-combination.Stereoelectronic reasons are made responsible for the failure of the intramolecular 1,2 and 1,3 proton shift in these systems.
- Maercker, Adalbert,Passlack, Michael
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p. 540 - 577
(2007/10/02)
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